QuantumGravity, is a theory which attempts to join the theories of quantum mechanics, and general relativity. The purpose of this theory is the creation of a single theory which outlines all fundamental forces. The benefits of this would be vast, as we would have a complete and unified theory to describe fundamental forces. The difficulty of creating such a theory is the fact that the foundation of the two two theories being united are polar opposites, making the situation far more complex.

Now that you know what both theories are created to do, you can see that the combination of all four fundamental forces would be a giant leap in the right direction for physics, however there is a significant, yet highly technical difference between the two. General relativity models gravity as a curvature within space-time that changes as mass moves. This is due to the principle in general relativity that there is no fixed space-time background. However, quantum mechanics, in most theories, depends on particle fields embedded in the flat space-time of special relativity, which is to say that there is a fixed space-time background. The practical reality of these two very different statements is that if we apply quantum physics to gravity, and discount the general relativity model, the gravitational particles will group together infinitely, making it impossible to currently compute.